HELP! e-620 + 50-200mm autofocus failure

I was recently in Cost Rica (highly recommended) and my e-620+50-200 combo was driving me crazy with its poor autofocus. I would like kind advice on what I was doing wrong and how I can fix it in the future. The following sequence is typical of how my camera was performing the entre trip. I missed countless shots while the lens racked back and forth, blowing right past the intended subject, only to produce this:

I realize the lighting is challenging (back-lit, dark, low-contrast subject, low light, lots of foreground and background contrast), but is such sub-optimal performance to be expected?

I am also getting a communication error between the camera body and the lens. The aperature shows up as " -.- " if the zoom is extended and the camera is powered on. I must power down, return the lens to 50mm, then cycle the power on and off. Randomly, communication will be restored and I can start shooting again. This never happens with my other lenses. Do you think this is related?